1. Field of the Invention
The present invention relates generally to a communication system, and in particular, to an apparatus and method to encode/decode block Low Density Parity Check (LDPC) codes.
2. Description of the Related Art
The next generation communication system has evolved into a packet service communication system, which is a system for transmitting burst packet data to a plurality of mobile stations, and is suitable for high-capacity data transmission. In order to increase the data throughput, a Hybrid Automatic Retransmission reQuest (HARQ) scheme and an Adaptive Modulation and Coding (AMC) scheme have been proposed. In order to use the HARQ scheme and the AMC scheme, the next generation communication system must support a variable code rate.
Generally, block LDPC codes, together with turbo codes, have high performance gain during high-speed data transmission and effectively correct errors caused by noise generated in a transmission channel, contributing to an increase in the reliability of the data transmission.
However, block LDPC codes are disadvantageous because they have a relatively high code rate, and are limited in terms of the code rate. Among the currently available block LDPC codes, the major block LDPC codes have a code rate of 1/2 and only minor block LDPC codes have a code rate of 1/3. The limitation in the code rate exerts a fatal influence on the high-speed, high-capacity data transmission. Although a degree of distribution representing the optimal performance can be calculated using a density evolution scheme in order to implement a relatively low code rate for block LDPC codes, it is difficult to implement a block LDPC code having a degree of distribution representing the optimal performance due to various restrictions, such as a cycle structure in a factor graph and hardware implementation.
In view of the code rate limitations for block LDPC codes, it is necessary to support a variable code rate, from low code rate to high low code rate, in order to transmit/receive signals.